H0LiCOW

H0 Lenses in COSMOGRAIL's Wellspring.

We measure the current expansion rate of the Universe using time-delay strong lensing.
And it works!

Latest Results

The H0LiCOW collaboration has revealed its measurement of the Hubble constant H0 from
its blind analysis of four multiply-imaged quasar systems through strong gravitational lensing: H0 = 72.5 +2.1−2.3 km/s/Mpc, at 3% precision, in the standard flat ΛCDM model.

This measurement is completely independent of, and in agreement with, the local distance ladder
measurements of H0. On the other hand, it is higher than the most recent Cosmic Microwave Background
predictions in flat-ΛCDM, as well as galaxy clustering combined to weak lensing, potentially pointing towards new physics beyond the predictions of
the standard cosmological model.

News & Press

"By using galaxies as giant gravitational lenses, an international group of astronomers using the NASA/ESA Hubble Space Telescope have made an independent measurement of how fast the Universe is expanding. The newly measured expansion rate for the local Universe is consistent with earlier findings. These are, however, in intriguing disagreement with measurements of the early Universe. This hints at a fundamental problem at the very heart of our understanding of the cosmos..."

Publications

H0LiCOW I. H0 Lenses in COSMOGRAIL’s Wellspring: Program Overview.

Strong gravitational lens systems with time delays between the multiple images allow measurements of time-delay distances, which are primarily sensitive to the Hubble constant that is key to probing dark energy, neutrino physics, and the spatial curvature of the Universe, as well as discovering new physics. We present H0LiCOW (H0 Lenses in COSMOGRAIL’s Wellspring), a program that aims to measure H0 with <3.5% uncertainty from five lens systems (B1608+656, RXJ1131−1231, HE0435−1223, WFI2033−4723 and HE 1104−1805)...

Galaxies located in the environment or on the line of sight towards gravitational lenses can significantly affect lensing observables, and can lead to systematic errors on the measurement of H0 from the time-delay technique. We present the results of a systematic spectroscopic identification of the galaxies in the field of view of the lensed quasar HE0435−1223 using the W.M. Keck, Gemini and ESO-Very Large telescopes. Our new catalog triples the number of known galaxy redshifts in the vicinity of the lens, expanding to 100 the number of measured redshifts for galaxies separated by less than 3' from the lens...

H0LiCOW III. Quantifying the effect of mass along the
line of sight to the gravitational lens HE0435−1223 through weighted galaxy counts.

Based on spectroscopy and multiband wide-field observations of the gravitationally
lensed quasar HE0435−1223, we determine the probability distribution function of the external convergence κext for this system. We measure the under/overdensity of the line of sight towards the lens system and compare it to the average line of sight throughout the universe, determined by using the CFHTLenS as a control field. Aiming to constrain κext as tightly as possible, we determine under/overdensities using various combinations of relevant informative weighing schemes for the galaxy counts, such as projected distance to the lens, redshift, and stellar mass...

H0LiCOW IV. Lens mass model of HE0435−1223 and blind measurement of its time-delay distance for cosmology.

Strong gravitational lenses with measured time delays between the multiple images allowa directmeasurement of the time-delay distance to the lens, and thus ameasure of cosmological parameters, particularly the Hubble constant, H0. We present a blind lens model analysis of the quadruply-imaged quasar lens HE0435−1223 using deep Hubble Space Telescope imaging, updated time-delay measurements from the COSmological MOnitoring of GRAvItational Lenses (COSMOGRAIL), ameasurement of the velocity dispersion of the lens galaxy based on Keck data, and a characterization of the mass distribution along the line of sight...

H0LiCOW V. New COSMOGRAIL time delays of HE0435−1223: H0 to 3.8% precision from strong lensing in a flat ΛCDM model.

We present a new measurement of the Hubble Constant H0 and other cosmological parameters based on the joint analysis of three multiply-imaged quasar systems with measured gravitational time delays. First, we measure the time delay of HE0435-1223 from 13-year light curves obtained as part of the COSMOGRAIL project. Companion papers detail the modeling of the main deflectors and line of sight effects, and how these data are combined to determine the time-delay distance of HE 0435-1223. Crucially, the measurements are carried out blindly with respect to cosmological parameters in order to avoid confirmation bias...

The empirical correlation between the mass of a super-massive black hole (MBH) and its host galaxy properties is widely considered to be evidence of their co-evolution. A powerful way to test the co-evolution scenario and learn about the feedback processes linking galaxies and nuclear activity is to measure these correlations as a function of redshift. Unfortunately, currently MBH can only be estimated in active galaxies at cosmological distances. At these distances, bright active galactic nuclei (AGN) can outshine the host galaxy, making it extremely difficult to measure the host’s luminosity...

Strongly lensed active galactic nuclei (AGN) provide a unique opportunity to make progress in the study of the evolution of the correlation between the mass of supermassive black holes and their host galaxy luminosity. We demonstrate the power of lensing by analyzing two systems for which state-of-the-art lens modelling techniques have been applied to deep Hubble Space Telescope imaging data. We use the reconstructed images to infer the total and bulge luminosity of the host and {published broad-line spectroscopy to estimate the black hole mass using the so-called virial method. We then combine our new measurements with new calibration of previously published measurements to study the evolution of the correlation out to z~4.5...

H0LiCOW VIII. Weak lensing mass reconstruction of HE0435-1223.

We present a weak gravitational lensing measurement of the external convergence along the line of sight to the quadruply lensed quasar HE0435-1223. Using deep r-band images from Subaru-Suprime-Cam we observe galaxies down to a 3 sigmas limiting magnitude of ~26 mags resulting in a source galaxy density of 14 galaxies per square arcmin after redshift-based cuts. Using an inpainting technique and Multi-Scale Entropy filtering algorithm, we find that the region in close proximity to the lens has an estimated external convergence of κext = -0.012 +0.020-0.013 and is hence marginally under-dense. We also rule out the presence of any halo with a mass greater than Mvir=1.6 x 1014 1/h MSol (68% confidence limit). Our results, consistent with previous studies of this lens, confirm that the intervening mass along the line of sight to HE0435-1223 does not affect significantly the cosmological results inferred from the time delay measurements of that specific object.

H0LiCOW IX. Cosmographic analysis of the doubly imaged quasar
SDSS 1206+4332 and a new measurement of the Hubble constant.

We present a blind time-delay strong lensing (TDSL) cosmographic analysis of the doubly
imaged quasar SDSS 1206+4332. We combine the relative time delay between the quasar
images, Hubble Space Telescope imaging, the Keck stellar velocity dispersion of the lensing
galaxy, and wide-field photometric and spectroscopic data of the field to constrain two angular
diameter distance relations. The combined analysis is performed by forward modelling the
individual data sets through a Bayesian hierarchical framework, and it is kept blind until the
very end to prevent experimenter bias. After unblinding...

Downloads

Paper II provides a catalog of all spectroscopically identified targets in the field of view of HE0435-1223, as well as 1-D spectra for targets observed with the VLT, Gemini and Keck telescopes. Those data are available as a single tar.gz file.

Paper V presents the 13-years optical light curves of HE0435-1223, as well as mock light curves created with PyCS in order to estimate the error on the time-delay measurement. Both can be downloaded here.